Air bag-use gas generator and air bag device

ABSTRACT

A gas generator for an air bag having a simple structure, which is activated to apply as small an impact as possible to a vehicle occupant at the initial stage of activation and, thereafter, can reliably protect the vehicle occupant by rapidly increasing gas pressure, is provided. It is a gas generator for an air bag in which an inner cylindrical member is disposed in the housing to define an ignition means accommodating chamber and a combustion chamber, plural flame-transferring holes for communicating the both chambers with each other are formed on the circumferential surface of the inner cylindrical member, and the plural flame-transferring holes are formed at a distance of less than 30% of the axial length of the inner cylindrical member, from an end of the inner cylindrical member. A gas generator, which can use even a gas generating agent with less ignitability, and further can exhibit enough operation performance at the initial stage of activation even when using such a gas generating agent, is provided. It is a gas generator for an air bag in which an inner cylindrical member is disposed in the housing to define an ignition means accommodating chamber and a combustion chamber, and the central angle formed by the adjacent communicating portions which are formed on the circumferential surface of the inner cylindrical member is adjusted to be not more than 60 degrees.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/11575 which has an Internationalfiling date of Dec. 27, 2001, which designated the United States ofAmerica.

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS

The present invention relates to a gas generator for an air bag forprotecting a vehicle occupant from the impact, particularly, to a gasgenerator for an air bag characterized in its operation performance, andan air bag apparatus.

RELATED ART

In a vehicle such as an automobile, in order to prevent the passengerfrom crashing into a hard portion inside the vehicle such as a steeringwheel and a windshield due to an inertia and being injured or dying whenthe vehicle collides at a high speed, an air bag system, which inflatesan air bag rapidly with a gas to protect the passenger from collidingwith such a dangerous portion, is provided.

It is desirable that such an air bag system can safely restrain thevehicle occupant even when the frame of the vehicle occupant (forexample, whether a sitting height is high or low, whether an adult or achild, and the like), a sitting attitude (for example, an attitude ofholding on the steering wheel) and the like are different. Then, therehas been conventionally suggested an air bag system which is activated,applying the impact to the passenger as small as possible at the initialstage of the activation.

JP-A 8-207696 suggests using two kinds of gas generating agent capsulesfor generating a gas at two stages comprising a first stage in which anair bag is inflated relatively slowly and a second stage in which a gasis generated rapidly. However, in this art, there is a defect that theinterior structure of the gas generator is complicated and the size ofthe container is made large, which results in factors of increasing acost.

Also in U.S. Pat. No. 4,998,751 and U.S. Pat. No. 4,950,458, in order torestrict the operation performance of the gas generator, it is proposedto provide two combustion chambers and burn the gas generating agent attwo stages. However, the structure is complicated and it is notsatisfactory yet.

In addition, relating to the activation of the gas generator, it needsto be rapidly activated just after the collision of the vehicle andproduce a cushion between the vehicle occupant and the vehicle beforethe vehicle occupant collides with structures in the vehicle.

For that reason, a gas generator, which is quickly activated by anactivation signal received from a sensor having detected the impact, andthat rapidly generates an enough amount of gas for inflating an air bag,is demanded.

Such a problem has already been solved by many gas generators providedso far, too.

However, the gas generators provided so far could not give enoughoperation performance when the characteristics of a gas generating agentused (for example, combustion performance) are changed, since they aredesigned with respect to each gas generating agent used in them, thatis, they are designed for the composition producing an operation gas foractually inflating an air bag.

DISCLOSURE OF THE INVENTION

The present invention provides a gas generator for an air bag which issimple in construction, is activated to apply as small an impact aspossible to a vehicle occupant at the initial stage of activation and,at a subsequent activation stage, can reliably protect the vehicleoccupant. For a gas generator for the driver side, for example, thisinvention provides a gas generator for an air bag exhibiting anoperation performance such that the inflation speed of the air bagduring a period of 10 milliseconds from the start of activation of thegas generator is moderated, compared with the conventional inflator, andat 30 to 50 milliseconds after the activation, the vehicle occupant isrestrained well. Also, this invention provides an air bag apparatususing this gas generator.

The above objective of this invention is achieved by a gas generator foran air bag comprising, in a housing having a gas discharging port, asubstantially cylindrical inner cylindrical member disposed in thehousing, an ignition means accommodating chamber formed inside the innercylindrical member, a combustion chamber formed outside the innercylindrical member, and plural flame-transferring holes formed on thecircumferential surface of the inner cylindrical member to communicatethe ignition means accommodating chamber with the combustion chamber,wherein the plural flame-transferring holes are formed at a distance ofless than 30% of the axial length of the inner cylindrical member, froman end of the inner cylindrical member. The plural flame-transferringholes are preferably formed at a distance of within 25% of the axiallength of the inner cylindrical member, from an end of the innercylindrical member.

The inner cylindrical member is disposed inside the housing and definesthe ignition means accommodating chamber in the inside and thecombustion chamber in the outside. At least, an ignition meansaccommodating chamber needs to be defined inside the inner cylindricalmember, however, it is possible to provide another chamber, for examplea combustion chamber (that is, a second combustion chamber) existingseparately from the combustion chamber existing outside the innercylindrical member. The ignition means accommodating chamber is achamber for accommodating an ignition means for activating the gasgenerator, and the combustion chamber is a chamber for accommodating agas generating means ignited and burnt by the activated ignition means.And, the flame-transferring hole is a penetrating hole to discharge aflame of the ignition means for igniting the gas generating means into acombustion chamber. Also, this inner cylindrical member includes amember having a flange at the end opening, as long as it has acylindrical circumferential wall surface.

In the present invention above, an igniter, which is activated when anignition electric current for activation is applied, is accommodated inthe one end side of the inner cylindrical member disposed in thehousing, and plural flame-transferring holes can be formed in the endbeing opposite to the igniter, divided with respect to the axial centerof the inner cylindrical member.

In addition, the gas generator of this invention can comprise, in ahousing having a gas discharging port, a substantially cylindrical innercylindrical member disposed in the housing, an ignition meansaccommodating chamber for accommodating an ignition means defined insidethe inner cylindrical member, a combustion chamber for accommodating agas generating agent defined outside the inner cylindrical member, andplural communicating portions formed circumferentially on thecircumferential surface of the inner cylindrical member to communicatethe ignition means accommodating chamber with the combustion chamber,wherein the central angle formed by the adjacent communicating portionscan be more than 60 degrees.

The above gas generator is usually formed such that, when the ignitionmeans disposed in the ignition means accommodating chamber is activated,it generates a flame and the flame is ejected into the combustionchamber through the plural flame-transferring holes formed on thecircumferential surface of the inner cylindrical member.

Then, in order to solve the above problem, the present inventionprovides a gas generator for an air bag in which ejecting angle of aflame ejecting through the flame-transferring holes is adjusted.

In other words, there is provided a gas generator for an air bagcomprising, in a housing having a gas discharging port, a substantiallycylindrical inner cylindrical member disposed in the housing, anignition means accommodating chamber for accommodating an ignition meansdefined inside the inner cylindrical member, a combustion chamber foraccommodating a gas generating agent defined outside the innercylindrical member, and plural flame-transferring holes formedcircumferentially in the circumferential surface of the innercylindrical member to eject a flame generated by activation of theignition means into the combustion chamber, wherein theflame-transferring holes eject the flame into the combustion chamber atan elevation angle and a depression angle of 45 degrees.

According to the present invention described above, there can beprovided a gas generator which is activated to apply as small an impactas possible to a vehicle occupant at the initial stage of activation andcan reliably protect the occupant at a subsequent activation stage.

Concretely, the operation performance of the gas generator can beadjusted such that the tank pressure measured at 0.25×T milliseconds isnot more than 0.25×P(kPa) when a predetermined maximum tank pressure isP(kPa) and a period of time from the start of rising of the tankpressure to the time when the maximum tank pressure P(kPa) has beenreached is T milliseconds in tank combustion test. This operationperformance is preferably adjusted further such that the tank pressuremeasured at 0.80×T milliseconds is not less than 0.70×P(kPa).

Also, in the gas generator of the present invention, it is preferablethat the peak of a pressure inside the housing during the activation ofthe gas generator is obtained at 10 to 20 milliseconds after theignition electric current is applied. That is, the pressure inside thehousing preferably reaches its maximum at 10 to 20 milliseconds afterthe ignition electric current is applied.

In the gas generator of the present invention, the combustion gas of thegas generating agent is discharged gradually from the gas dischargingport to increase the pressure of the gas generator and to slowlyincrease the pressure in the tank, before the peak of the maximumcombustion pressure inside the housing, which is before 10 to 20milliseconds after the ignition electric current is applied. After thepressure inside the housing of the gas generator reaches its peak, asufficient amount of a gas to restrain the vehicle occupant is rapidlydischarged from the gas discharging port to lower the pressure in thegas generator and at the same time, to sharply increase the pressure inthe tank. Such a gas generator is realized by a gas generator having theoperation performance adjusted such that the tank pressure measured at0.25×T milliseconds is not more than 0.25×P(kPa) when a predeterminedmaximum tank pressure is P(kPa) and a period of time from the start ofrising of the tank pressure to the time when the maximum tank pressureP(kPa) has been reached is T milliseconds in tank combustion test. Inthe gas generator of this invention having such an operationperformance, the output at the initial stage of activation issuppressed, so that the airbag (bag body) accommodated in the module canbe prevented from rapidly inflating at the initial stage of activationand from applying excess impacts to the vehicle occupant. To thecontrary to this, when the tank pressure measured at 0.25×T millisecondsis not less than 0.25×P (kPa), the inflation force of the air bag at thetime of breaking the module may be too strong depending on the operationcircumstance (for example, outside air temperature), whereby making itdifficult to obtain the aimed effect of the invention.,

In the gas generator for an air bag of the present invention, at leastthe flame-transferring hole, which is formed in the inner cylindricalmember defining the combustion chamber and the ignition meansaccommodating chamber in the housing, needs to be formed not in thecenter but on either end side of the inner cylindrical member, however,other configuration than this, for example, a composition and shape of agas generating means, the existence of a coolant or a filter for coolingand/or purifying an operation gas generated by the combustion of gasgenerating means, the whole shape of the housing, and so on can beadjusted appropriately according to the operation performance. Forexample, as to the gas generating means to be burnt and generate anoperation gas, besides azide type gas generating agent based oninorganic azides which have conventionally been used widely, forexample, sodium azide, it is possible to use non-azide type gasgenerating agent not based on inorganic azide etc. Also, size and numberof gas discharging ports formed in the housing, the size and whole shapeof housing, and so on can be adjusted appropriately according tooperation performance and accommodating space.

The above gas generator for an air bag is accommodated in the modulecase together with an air bag (bag body) to introduce a gas generated inthe gas generator to inflate, thereby being an air bag apparatus. Inthis air bag apparatus, the gas generator is activated upon the impactsensor detecting the impact to discharge an operation gas from the gasdischarging port of the housing. The operation gas flows into the airbag, and thereby the air bag inflates to break a module cover and formsa cushion absorbing the impact between a hard structure in the vehicleand an occupant.

The gas generator of the present invention provides a gas generator foran air bag which is simple in structure and that is activated to applyas small an impact as possible to a vehicle occupant at the initialstage of activation and can reliably protect the vehicle occupant byinflating the air bag rapidly at a subsequent activation stage.

Next, the present invention provides a gas generator for an air baghaving a structure capable of using even a gas generating agent whoseignitability is less than a gas generating agent conventionally used ingas generators. That is, it provides a gas generator which can exhibitsatisfactory operation performance at the initial stage of operationeven when it uses such a gas generating agent. Also, an air bagapparatus using this gas generator is provided.

The above objective of this invention is achieved by an gas generatorfor an air bag comprising, in a housing having a gas discharging port, asubstantially cylindrical inner cylindrical member disposed in thehousing, an ignition means accommodating chamber for accommodating anignition means defined inside the inner cylindrical member, a combustionchamber for accommodating a gas generating agent defined outside theinner cylindrical member, and plural flame-transferring holes formed onthe circumferential surface of the inner cylindrical member to eject aflame generated by the activation of the ignition means into a firstcombustion chamber, wherein the flame-transferring holes are formed at adistance of 30% to 70% of the axial length of the inner cylindricalmember, from an end of the inner cylindrical member.

The objective of the present invention is achieved also by a gasgenerator comprising plural communicating portions formedcircumferentially on the circumferential surface of the innercylindrical member to communicate the ignition means accommodatingchamber with the combustion chamber, wherein the central angle formed bythe adjacent communicating portions is adjusted to be not more than 60degrees, preferably not more than 45 degrees.

The inner cylindrical member above is disposed inside the housing todefine the ignition means accommodating chamber in the inside and thecombustion chamber in the outside. Therefore, at least an ignition meansaccommodating chamber needs to be arranged inside the inner cylindricalmember, but further another chamber such as a combustion chamber (thatis, a second combustion chamber) existing separately from the combustionchamber existing outside the inner cylindrical member can be provided.The ignition means accommodating chamber is a chamber for accommodatingan ignition means to activate the gas generator, and the combustionchamber is a chamber for accommodating a gas generating means ignitedand burnt by the activated ignition means. And the flame-transferringholes are penetrating holes to eject a flame of the ignition means forigniting the gas generating means into a combustion chamber. Also, theinner cylindrical member contains one having a flange at the endopening, as long as it has a cylindrical circumferential wall surface.

These communicating portions can comprise one or at least twoflame-transferring holes radially penetrating in the inner cylindricalmember. That is, for example, when a single flame-transferring holebecomes a communicating portion, the communicating portion become theflame-transferring hole substantially. However, when each penetratingportion comprises the plural flame-transferring holes, so-called groupsof the flame-transferring holes comprising the plural flame-transferringholes are formed circumferentially in the inner cylindrical member withthe above predetermined intervals.

Especially, when the communicating portion comprises a singleflame-transferring hole, this flame-transferring hole is desirablyformed to have the inner diameter of 1 to 4 mm, preferably 1.8 to 3.2mm.

Further, in the above gas generator, an ejecting angle of a flame orheat mist of the ignition means ejected from the plural communicatingportions is preferably adjusted to be in the range of horizontal anglewhich is not less than 60 degrees, and preferably not less than 90degrees, having the center as the axis perpendicular to the center ofthe communication portion.

The above problem can be also solved by a gas generator in which theinternal pressure of the housing reaches its maximum at 5 to 20milliseconds after the ignition electric current is applied at the timeof the activation. In this case, the surface area of gas generatingagent, which is ignited at 2 milliseconds after the ignition electriccurrent is applied to the igniter, is preferably 30 to 90% and more, andmore preferably 40 to 60% and more of the total surface area of the gasgenerating agent accommodated originally in the combustion chamber.

According to the above gas generator of the present invention, by aflame of ignition means ejected from the communication portion, the gasgenerating agent accommodated in the combustion chamber can be ignitedat once to start combustion. That is, the ignitability of gas generatingagent can be improved at the initial stage of the activation of the gasgenerator can be improved.

In the gas generator for an air bag of the present invention, at leastthe inner cylindrical member for defining the combustion chamber and theignition means accommodating chamber in the housing needs to bedisposed, and as to communication portions formed circumferentially onthe circumferential surface of the inner cylindrical member and capableof communicating both chambers with each other, the central angle formedby the adjacent communicating portions needs to be adjusted to be notmore than 60 degrees, however, other configuration than this, forexample, a composition and shape of a gas generating means, theexistence of a coolant or a filter for cooling and/or purifying anoperation gas generated by the combustion of gas generating means, thewhole shape of the housing, and so on can be adjusted appropriatelyaccording to the operation performance. For example, as to the gasgenerating means to be burnt and generate an operation gas, besidesazide type gas generating agent based on inorganic azides which haveconventionally been used widely, for example sodium azide, it ispossible to use non-azide type gas generating agent not based oninorganic azide etc. Also, a size and number of gas discharging portsformed in the housing, a size and whole shape of housing, and so on canbe adjusted appropriately according to operation performance and anaccommodating space.

The above gas generator for an air bag is accommodated in the modulecase together with an air bag (bag body) to introduce a gas generated inthe gas generator to inflate, thereby being an air bag apparatus. Inthis air bag apparatus, the gas generator is activated upon the impactsensor detecting the impact to discharge an operation gas from the gasdischarging port of the housing. The operation gas flows into the airbag, and thereby the air bag inflates to break a module cover and formsa cushion absorbing the impact between a hard structure in the vehicleand an occupant.

The present invention is a gas generator for an air bag having astructure capable of using even a gas generating agent with lowignitability, and further, it can be a gas generator which can exhibitsatisfactory operation performance at the initial stage of activationeven when it uses such a gas generating agent. That is, even when thecharacteristics of gas generating agent used (such as combustionperformance) is changed, a gas generator which exhibits initialoperation performance or similar thereto is realized.

Further, a gas generator having such an effect is realized through asimple structure.

The operation performance of the above gas generator can be confirmed bymeans of tank combustion test described below.

Tank Combustion Test

A gas generator for an air bag is fixed in a SUS (stainless steel) tankhaving the internal volume of 60 liters. After the tank is hermeticallyclosed at a room temperature, the gas generator is connected to anexternal ignition electric circuit. A pressure transducer installed inthe tank separately is used to measure a change in the increasingpressure in the tank for the duration from 0 to 200 milliseconds, withthe moment at which the ignition electric circuit switch is turned on(the ignition current is applied) taken as time 0(zero). The measureddata are then processed by a computer to generate a tank pressure/timecurve (hereinafter referred to as a “tank curve”) which is used toevaluate the performance of the gas generator. After the combustion isover, part of the gas in the tank may be sampled for submitting toanalysis of CO, NOx and so on.

Similarly, a change in the increasing pressure inside the housing ismeasured for the duration from 0 to 200 milliseconds, with the moment atwhich the ignition electric current is applied taken as time 0 (zero),to obtain the change with time of the pressure inside the housing. Usingthis, the time until the pressure inside the housing becomes itsmaximum, that is, the time to the maximum internal pressure can bespecified.

The tank maximum pressure in this invention means the maximum pressurein the SUS tank during the tank combustion test, and the maximuminternal pressure is the maximum pressure in the housing when the gasgenerator is activated (that is, maximum internal pressure in thehousing).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross sectional view showing oneembodiment of the gas generator for an air bag of the present invention.

FIG. 2 is a schematic drawing showing an air bag apparatus of thepresent invention.

FIG. 3 is a tank curve of a tank test shown in the Example.

FIG. 4 is principal part of a horizontal cross section of the gasgenerator shown in the FIG. 1.

Explanation of Reference Numerals

-   1 Diffuser Shell-   2 closure shell-   3 housing-   4 igniter-   5 transfer charge-   6 gas generating agent-   7 coolant/filter    Embodiment 1 of the Invention

The housing of the gas generator for an air bag of the present inventionand the gas generator for an air bag using the same will be explained asfollows according to the embodiments shown in the figures.

FIG. 1 is a schematic vertical cross section showing one embodiment ofthe gas generator for an air bag of the present invention.

The gas generator shown in this figure contains, in the housing 3 havinga gas discharging port 11, an ignition means comprising an electric typeigniter 6 and a transfer charge 7, and a gas generating means whichgenerates an operation gas to inflate an air bag by activation of theignition means (that is, a gas generating agent 8), and further acoolant/filter means (that is, a coolant 5) to cool an operation gasgenerated by combustion of the gas generating agent 8 is disposedbetween the combustion chamber 9 in which the gas generating agent 8 isaccommodated and a circumferential wall portion of the housing 3. And, adeflecting member 18 having a cylindrical portion 19 is disposed at theend portion in the diffuser shell 1 side of coolant 5.

The housing 3 is formed from a diffuser shell 1 having a cylindricalshape with a top and a closure shell 2 having a cylindrical shape with abottom, and both shells are integrated by welding at outward flangeportions 53 and 58 formed at each opening. Between these, acircumferential wall of the closure shell is formed to expand outwardlyin the radial direction at the flange portion 58 side.

In the housing, a inner cylindrical member 4 having a flange portion 24jointed to the interior surface of the housing ceiling portion isdisposed, and the inside of the inner cylindrical member 4 becomes anignition means accommodating chamber 10 and the outside thereof becomesa combustion chamber 9. Both chambers are formed to communicate witheach other through aflame-transferring hole 14 provided on acircumferential surface of the inner cylindrical member 4. The ignitionmeans accommodating chamber 10 accommodates an ignition means comprisingan igniter 6 which receives an activation signal (that is, an ignitionelectric current for activation) to activate, and a transfer charge 7ignited and burnt by the activation of the igniter. Also, the combustionchamber 9 accommodates a gas generating agent 8 which is ignited andburnt by a flame of the ignition means (a flame of the transfer charge 7in this embodiment) to generate an operation gas for inflating an airbag.

The igniter 6 constituting the ignition means is fixed at the bottom endby crimping a bottom end opening of inner cylindrical member 4, and thetransfer charge 7 is disposed directly over the igniter 6. And, aflame-transferring hole 14 formed on a circumferential surface of theinner cylindrical member 4 is provided in the opposite side of theigniter side in the inner cylindrical member (that is, in the transfercharge 7 side in the figure). In this embodiment, the flame-transferringhole 14 is formed at a distance of less than 30% of the axial length ofthe inner cylindrical member 4, from the end in the side where theflange is formed.

A gas generating agent is ignited by a flame or heat mist of transfercharge ejected from the flame-transferring hole 14. And, as describedabove, by adjusting the position (height) at which flame-transferringholes are formed, the ignited area of a gas generating agent at 2milliseconds after the ignition electric current is applied can beadjusted. For example, when the axial length of the inner cylindricalmember is about 29 mm and the flame-transferring holes are formed at adistance of 7 mm from the end surface of the flange portion, it isestimated that 50% of the total surface area of the originally loadedgas generating agent is ignited at 2 milliseconds after the ignitionelectric current is applied.

The inner cylindrical member 4 whose end portion is crimped to fix theigniter 6 is received by an opening portion 60 of the closure shell 2described below, and is integrated with closure shell 2 by welding in astate of fixing the igniter 6. Concretely, a round portion 61 bendinginwardly into the housing 3 is formed integrally with the openingportion 60, and this round portion 61 and the inner cylindrical member 4are welded. Because of the round portion 61 bent inwardly into thehousing 3, it is avoided that only the round portion 61 protrudesaxially out of the housing 3, and, to that extent, the total height ofthe housing 3 itself can be suppressed, and furthermore, the totalheight of the gas generator can be suppressed. Alternatively, when a gasgenerator formed in this manner has the same height as the height of agas generator in which a round portion 61 is bent towards the outside ofthe housing 3, a larger inner volume of the housing can be obtained withthe same height and the outer diameter. Further, the round portion 61can support a substantially circular underplate 22 supporting a gasgenerating means.

The cylindrical coolant 5 made of a laminated wire mesh and the like issupported by bent portions formed at end portions of the respectiveshells 1 and 2, and disposed to face practically the innercircumferential surface of the housing. And, between the outercircumferential surface of this coolant 5 and the inner circumferentialsurface of the housing 3, a space 20 which serves as a flow path of anoperation gas is obtained. By this space 20, the whole coolant 5 canwork effectively.

As the coolant 5, it is preferable not to swell radially and outwardlydue to the pressure of passing an operation gas. The reason is that, ifthe coolant 5 swells due to passing of the gas generating means, thespace 20 secured between the coolant 5 and the inner circumferentialsurface of the housing is blocked, and can not effectively function as agas flow-path. Hence, the coolant 5 shown in this embodiment is formedto have a tensile strength in the radial direction of 12,054N (1,230kgf).

A deflecting member 18 is disposed between the end surface of thiscoolant 5 and the inner surface of the diffuser shell 1. This deflectingmember 18 is effective in case of using the gas generating agent 8 thatproduces fluid or semifluid combustion products after combustion.

The reason is that, combustion products generated by combustion of thegas generating agent can be removed by the cylindrical portion 19 of thedeflecting member 18 which makes the combustion products adhere theretoor crash thereinto to drop them. Also, in the deflecting member 18, acircular portion 16 which abuts against the end surface of coolant 5 isformed to have an appropriate elasticity, so that the coolant 5 which isformed from wire mesh and has little elasticity in the axial directioncan be used as the coolant 5 disposed radially outside the combustionchamber 9. Further, in deflecting member 18, a wall portion 17 abuttingagainst an inner circumferential surface of the coolant 5 is formedintegrally with the circular portion 16. With this, the coolant 5 can belocated and fixed, and additionally, so-called short-pass in which anoperation gas is discharged without passing through the coolant can beprevented.

In the gas generator formed as described above, the transfer charge 7 isignited and burnt by the igniter 6 activated by the application of theignition electric current for activation, and the flame thereof isreleased, through the flame-transferring hole 14 in inner cylindricalmember 4, into the accommodating space for gas generating agent 8. Theflame of the transfer charge 7 is to ignite and burn the gas generatingagent 8. And even when part of the flame passes directly through thecoolant 5, it crashes into the cylindrical portion 19 of the deflectingmember 18, and thereby, the flame can never be ejected directly throughthe gas discharging port 11. The operation gas generated by the gasgenerating agent 8 which is ignited by the flame of the transfer charge7 passes through the coolant 5 and reaches the space 20 secured betweenthe outer circumferential surface of the coolant 5 and the innercircumferential surface of the housing 3. If fluid or semifluidcombustion products are included in the operation gas having passedcoolant 5, those products crash and adhere to the cylindrical portion 19of the deflecting member 18 arranged in the space 20, and they areremoved from the operation gas.

Embodiment 2 of the Invention

The housing of the gas generator for an air bag of the present inventionand the gas generator for an air bag using the same will be explained asfollows according to the embodiments shown in the figures.

FIG. 1 is a schematic vertical cross section showing one embodiment ofthe gas generator for an air bag of the present invention.

The gas generator shown in this figure contains, in the housing 3 havinga gas discharging port 11, an ignition means comprising an electric typeigniter 6 and a transfer charge 7, and a gas generating means whichgenerates an operation gas to inflate an air bag by activation of theignition means (that is, a gas generating agent 8), and further acoolant/filter means (that is, a coolant 5) to cool an operation gasgenerated by combustion of the gas generating agent 8 is disposedbetween the combustion chamber 9 in which the gas generating agent 8 isaccommodated and a circumferential wall portion of the housing 3. And, adeflecting member 18 having a cylindrical portion 19 is disposed at theend portion in the diffuser shell 1 side of coolant 5.

The housing 3 is formed from a diffuser shell 1 having a cylindricalshape with a top and a closure shell 2 having a cylindrical shape with abottom, and both shells are integrated by welding at outward flangeportions 53 and 58 formed at each opening. Between these, acircumferential wall of the closure shell is formed to expand outwardlyin the radial direction at the flange portion 58 side.

In the housing, a inner cylindrical member 4 having a flange portion 24jointed to the interior surface of the housing ceiling portion isdisposed, and the inside of the inner cylindrical member 4 becomes anignition means accommodating chamber 10 and the outside thereof becomesa combustion chamber 9. Both chambers are formed to communicate witheach other through plural communicating portions provided on acircumferential surface of the inner cylindrical member 4. In thisembodiment, the communicating portions are realized by theflame-transferring hole 14, and each communicating portion comprises asingle flame-transferring hole 14 formed to have an inner diameter of1.8 to 3.2 mm. However, the communicating portion can comprise acombination of plural flame-transferring holes having a smaller diameter(as a group of the flame-transferring holes).

When this flame-transferring hole 14 is formed such that the distance(L) from the flame-transferring hole to the end of the inner cylindricalmember 4 is 30 to 70% of the axial length of the inner cylindricalmember (L1), ignitability of gas generating agent 8 can be improved. Forexample, as shown in FIG. 1, when an inner cylindrical member having theaxial length (L1) of 29 mm is used and a flame-transferring hole 14 isformed to position at 10 mm from the end in the diffuser shell side, aninternal pressure reaches the maximum at about 8.2 milliseconds afterthe ignition electric current is applied. The axial length of the innercylindrical member 4 is, in principle, based on a state in which it isdisposed in a gas generator. However, in most cases, no substantialdifference arises even though it is based on a state before being builtinto a gas generator.

And, the ignition means accommodating chamber 10 accommodates theignition means comprising the igniter 6, which receives an activationsignal (that is, an ignition electric current for activation) andactivate, and the transfer charge 7 ignited and burnt by activation ofthe igniter. The igniter 6 constituting the ignition means is fixed atthe bottom end by crimping an bottom end opening of inner cylindricalmember 4, and the transfer charge 7 is disposed directly over theigniter 6. Also, the combustion chamber 9 accommodates a gas generatingagent 8 which is ignited and burnt by a flame of the ignition means (aflame of the transfer charge 7 in this embodiment) to generate anoperation gas for inflating an air bag The flame-transferring hole 14formed on the circumferential surface of the inner cylindrical member 4is adjusted such that the central angle α (alpha) formed by the adjacentcommunicating portions is not more than 60 degrees, as shown in thehorizontal sectional view of the inner cylindrical member 4 in FIG. 4.By this, the interval between the adjacent flame-transferring holes 14can be made small, and a contacting area between a flame of the transfercharge ejected from the flame-transferring hole 14, and the gasgenerating agent in the combustion chamber can be increased. Thus, anignited area of the gas generating agent 8 at the initial stage ofactivation of the gas generator can be larger, and thereby, ignitabilityof the gas generating agent can be improved. When the communicatingportion comprises a single flame-transferring hole 14, for example, inthe inner cylindrical member 4, twelve (12) flame-transferring holes 14having the inner diameter of 1.85 mm can be formed in thecircumferential direction (that is, the central angle between theadjacent communicating portions is 30 degrees), eight (8)flame-transferring holes having the inner diameter of 2.2 mm can beformed in the circumferential direction (that is, the central anglebetween the adjacent communicating portions are 45 degrees), or six (6)flame-transferring holes 14 having the inner diameter of 2.6 mm can beformed in the circumferential direction (that is, the central anglebetween the adjacent communicating portions is 60 degrees).

In the communicating portions formed in this manner (theflame-transferring holes 14 in this embodiment), when the total area ofthe communicating holes is almost constant, the smaller the centralangle α (alpha) between the adjacent communicating portions becomes, themore improved is the initial ignitability of gas generating agent.

Also, a flame or heat mist of the ignition means (the transfer charge 7in this embodiment) which is ejected from the plural communicatingportions (the flame-transferring holes 14 in this embodiment) arepreferably adjusted to be ejected in the range of the horizontal angle β(beta) which is not less than 60 degrees having the center as the axis Lperpendicular to the center of the flame-transferring holes 14.

The inner cylindrical member 4 whose end portion is crimped to fix theigniter 6 is received by an opening portion 60 of the closure shell 2described below, and is integrated with closure shell 2 by welding in astate of fixing the igniter 6. Concretely, a round portion 61 bendinginwardly into the housing 3 is formed integrally with the openingportion 60, and this round portion 61 and the inner cylindrical member 4are welded. Because of the round portion 61 bent inwardly into thehousing 3, it is avoided that only the round portion 61 protrudesaxially out of the housing 3, and, to that extent, the total height ofthe housing 3 itself can be suppressed, and furthermore, the totalheight of the gas generator can be suppressed. Alternatively, when a gasgenerator formed in this manner has the same height as the height of agas generator in which a round portion 61 is bent towards the outside ofthe housing 3, a larger inner volume of the housing can be obtained withthe same height and the outer diameter. Further, the round portion 61can support a substantially circular underplate 22 supporting a gasgenerating means.

The cylindrical coolant 5 made of a laminated wire mesh and the like issupported by bent portions formed at end portions of the respectiveshells 1 and 2, and disposed to face practically the innercircumferential surface of the housing. And, between the outercircumferential surface of this coolant 5 and the inner circumferentialsurface of the housing 3, a space 20 which serves as a flow path of anoperation gas is obtained. By this space 20, the whole coolant 5 canwork effectively.

Preferably, the coolant 5 does not swell radially and outwardly due tothe pressure in passing an operation gas there through. The reason isthat, if the coolant 5 swells due to passing of the, operation gas, thespace 20 secured between the coolant 5 and the inner circumferentialsurface of the housing is blocked, and can not effectively function as agas flow-path. Hence, the coolant 5 shown in this embodiment is formedto have a tensile strength in the radial direction of 12,054N(1,230kgf).

A deflecting member 18 is disposed between the end surface of thiscoolant 5 and the inner surface of the diffuser shell 1. This deflectingmember 18 is effective in case of using the gas generating agent 8 thatproduces fluid or semifluid combustion products by combustion.

The reason is that, combustion products generated by combustion of thegas generating agent can be removed by the cylindrical portion 19 of thedeflecting member 18 which makes the combustion products adhere theretoor crash thereinto to drop them. Also, in the deflecting member 18, acircular portion 16 which abuts against the end surface of coolant 5 isformed to have an appropriate elasticity, so that the coolant 5 which isformed from wire mesh and has little elasticity in the axial directioncan be used as the coolant 5 disposed radially outside the combustionchamber 9. Further, in deflecting member 18, a wall portion 17 abuttingagainst an inner circumferential surface of the coolant 5 is formedintegrally with the circular portion 16. With this, the coolant 5 can belocated and fixed, and additionally, so-called short-pass in which anoperation gas is discharged without passing through the coolant can beprevented.

In the gas generator formed as described above, the transfer charge 7 isignited and burnt by the igniter 6 activated by the application of theignition electric current for activation, and the flame thereof isreleased, through the flame-transferring hole 14 in inner cylindricalmember 4, into the accommodating space for gas generating agent 8. Theflame of the transfer charge 7 is to ignite and burn the gas generatingagent 8. And even when part of the flame passes directly through thecoolant 5, it crashes into the cylindrical portion 19 of the deflectingmember 18, and thereby, the flame can never be ejected directly throughthe gas discharging port 11. The operation gas generated by the gasgenerating agent 8 which is ignited by the flame of the transfer charge7 passes through the coolant 5 and reaches the space 20 secured betweenthe outer circumferential surface of the coolant 5 and the innercircumferential surface of the housing 3. If fluid or semifluidcombustion products are included in the operation gas having passedcoolant 5, those products crash and adhere to the cylindrical portion 19of the deflecting member 18 arranged in the space 20, and they areremoved from the operation gas.

EXAMPLE 1

A tank test was conducted using the gas generator having the structureshown in FIG. 1. In this gas generator, an inner cylindrical memberhaving the axial length of 29 mm was used, and flame-transferring holes14 were formed to position at 7 mm from the end surface of flangeportion. And, these flame-transferring holes had the inner diameter of3.2 mm and 4 (four) holes in all were formed circumferentially with theinterval of 90 degrees. The tank curve thereof is shown in FIG. 3.

As evidenced by this FIG. 3, when a tank combustion test is conductedusing a gas generator of the present invention, the gas generator canexhibit the tank pressure measured at 0.25×T milliseconds of not morethan 0.25×P(kPa) and the tank pressure measured at 0.80×T millisecondsof not less than 0.70×P(kPa), when the maximum tank pressure is P(kPa)and a period of time from the start of rising of the tank pressure tothe time when the maximum tank pressure P(kPa) has been reached is Tmilliseconds.

EXAMPLE 2

A tank combustion test was conducted using a gas generator shown in FIG.1, and the time when the internal pressure of the housing reached themaximum (hereafter, also referred to as the time for the peak of themaximum internal pressure of the housing), after ignition electriccurrent had been applied, was measured.

And, in the inner cylindrical member defining the ignition meansaccommodating chamber and the combustion chamber, flame-transferringholes described in the following (1) or (2) were formed as communicatingportions which can make both chambers communicated with each other. Theresults are shown in FIG. 1.

And, the explanation of detail of the gas generator used in this exampleis omitted, with referring to the embodiment above.

-   (1) A gas generator in which 8 (eight) communicating portions    comprising flame-transferring holes (enhancer nozzles) having the    inner diameter of 2.2 mm were formed circumferentially in the inner    cylindrical member, with the central angle of 45 degrees between    adjacent communicating portions.-   (2) A gas generator in which 12 (twelve) communicating portions    comprising flame-transferring holes (enhancer nozzles) having the    inner diameter of 1.85 mm were formed circumferentially in the inner    cylindrical member, with the central angle of 30 degrees between    adjacent communicating portions.

The time when the internal pressure of the housing reached the maximum,which is obtained by using a gas generator shown in (1) or (2) above,were shown in Table 1.

TABLE 1 Time when the maximum of internal Central angle pressure of theInner diameter (mm) × between adjacent housing was number of flame-flame-transferring obtained transferring holes holes (degree)(milliseconds) φ2.2 × 8 45 16 φ1.85 × 12 30 14

As evidenced by these results, ignitability of the gas generating agentcan be improved by forming many communicating portions (theflame-transferring holes in this embodiment), that is, by decreasing thecentral angle between adjacent flame-transferring holes.

By this, a gas generator for an air bag which can inflate an air bagrapidly after the impact is realized.

However, the objective of this example is to confirm the improvement ofignitability of the gas generating agent according to a shape and anarrangement of the communicating portions (the flame-transferringholes). Thus, generally similar effect to these examples can beconfirmed by using gas generators in which a shape and an arrangement ofthe communicating portions (the flame-transferring holes) are differentas shown in (1) or (2) above and the other configurations are similar.That is, in confirming effects of the present invention, any gasgenerating agents can be used as the gas generating agent used in gasgenerators (1) or (2) above, as long as their gas outputs and linearburning rates are the same, and as long as a space volume in gasgenerators capable of contributing to combustion of gas generating agentare the same, similar effect can be confirmed.

Embodiment 3 of the Invention

In FIG. 1, the gas discharging port 11 and the flame-transferring hole14 are each sealed with a seal tape 15, and the gas generating agent 8is supported by the underplate 22 and is accommodated in the combustionchamber. Also, the member described as the deflecting member 18 in thisembodiment can function as a mist catching member or a flame preventingplate with the similar structure.

Embodiment 4 of the Invention

An example of an air bag apparatus of the present invention comprising agas generator using an electric ignition type igniter is shown in FIG.2.

This air bag apparatus comprises a gas generator 200, an impact sensor201, a control unit 202, a module case 203 and an air bag 204. As gasgenerator 200, the gas generator explained based on FIG. 1 is used, andthe operation performance thereof is adjusted such that it is activatedto apply as small an impact as possible to a vehicle occupant at theinitial stage of activation.

The impact sensor 201 may be, for example, a semiconductor typeacceleration sensor. The semiconductor type acceleration sensor has fourbridge-connected semiconductor strain gauges attached on a beam ofsilicon substrate that deflects when subjected to an acceleration.

When an acceleration is applied, the beam deflects causing strain on itssurface, which in turn change the resistance of the semiconductor straingauges. The change in resistance is to be detected as a voltage signalproportional to the acceleration.

The control unit 202 has an ignition decision circuit, which is suppliedwith a signal from the semiconductor type acceleration sensor. When theimpact signal from the sensor 201 exceeds a predetermined value, thecontrol unit 202 starts calculation. When the result of the calculationexceeds a predetermined value, the control unit outputs an activationsignal (that is, an ignition electric current for activation) to theigniter 6 of the gas generator 200.

The module case 203 is formed of, for example a polyurethane, andincludes a module cover 205. In this module case 203, the air bag 204and the gas generator 200 are accommodated to form a pad module. Thispad module, when mounted on the driver side, is normally installed in asteering wheel 207.

The air bag 204 is made of nylon (for example, nylon 66) or polyesterwith its bag inlet 206 surrounding the gas discharging ports of the gasgenerator. The air bag is folded and fixed to the flange portion of thegas generator.

When the semiconductor type impact sensor 201 detects the impact at thetime of collision of an automobile, the signal is sent to the controlunit 202, which, when the impact signal from the sensor exceeds apredetermined value, starts a calculation. If the result of thecalculation exceeds a predetermined value, the control unit outputs anactivation signal to the igniter 6 of the gas generator 200. The igniter4 is then activated to ignite and burn the gas generating agent toproduce a gas. The gas is ejected into the air bag 204, causing the airbag to inflate with breaking the module cover 205, thereby forming ashock-absorbing cushion between the steering wheel 207 and the vehicleoccupant.

1. A gas generator for an air bag comprising: a housing having a gasdischarging port; a substantially cylindrical inner cylindrical memberdisposed in the housing, an ignition means accommodating chamber definedinside the inner cylindrical member, a combustion chamber definedoutside the inner cylindrical member; and plural flame-transferringholes formed in the circumferential surface of the inner cylindricalmember to communicate the ignition means accommodating chamber with thecombustion chamber, wherein the plural flame-transferring holes areformed at a distance of less than 30% of the axial length of the innercylindrical member, from an end of the inner cylindrical member, theflame-transferring hole is formed to have the inner diameter of 1 to 4mm, and the flame-transferring holes are formed radially on thecircumferential surface of the inner cylindrical member, and the centralangle formed by the adjacent flame-transferring holes being not lessthan 60 degrees.
 2. The gas generator for an air bag according to claim1, wherein the plural flame-transferring holes are formed at a distanceof less than 25% of the axial length of the inner cylindrical member,from an end of the inner cylindrical member.
 3. The gas generator for anair bag according to claim 1 or 2, wherein an igniter, which isactivated when an ignition electric current for activation is applied,is accommodated in one axial end side of the inner cylindrical member,and the plural flame-transferring holes are formed in the end beingopposite, divided at the center of the axis of the inner cylindricalmember.
 4. The gas generator for an air bag according to claim 1,wherein the ignition means accommodating chamber accommodates anignition means including an igniter which is activated when an ignitionelectric current is applied, the flame-transferring holes are forejecting a flame generated by activation of the ignition means into thecombustion chamber, and the flame-transferring holes eject a flame of atransfer charge with horizontal angle of more than 60 degrees, havingthe perpendicular axis as a center.
 5. The gas generator for an air bagaccording to claim 1, wherein the ignition means accommodating chamberaccommodates an ignition means including an igniter which is activatedwhen an ignition electric current is applied, and the operationperformance thereof is adjusted such that the tank pressure measured at0.25×T milliseconds is not more than 0.25×P(kPa) when the maximum tankpressure is P(kPa), and a period of time from the start of rising of thetank pressure to the time when the maximum tank pressure P(kPa) has beenreached is T milliseconds in tank combustion test.
 6. The gas generatorfor an air bag according to claim 1, wherein the ignition meansaccommodating chamber accommodates an ignition means, including anigniter which is activated when an ignition electric current is applied,and the operation performance thereof is adjusted such that the tankpressure measured at 0.80×T milliseconds is not less than 0.70×P(kPa)when the maximum tank pressure is P(kPa), and a period of time from thestart of rising of the tank pressure to the time when the maximum tankpressure P(kPa) has been reached is T milliseconds in tank combustiontest.
 7. The gas generator for an air bag according to claim 1, whereinthe ignition means accommodating chamber accommodates an ignition meansincluding an igniter which is activated when an ignition electriccurrent is applied, the combustion chamber accommodates a gas generatingagent ignited and burnt by activation of the ignition means to generatea combustion gas, and the pressure inside the housing reaches itsmaximum at 10 to 20 milliseconds after the ignition electric current isapplied.
 8. The gas generator for an air bag according to claim 1,wherein the ignition means accommodating chamber accommodates anignition means including an igniter which is activated when an ignitionelectric current is applied, the plural flame-transferring holes areformed to eject a flame generated by activation of the ignition meansinto the combustion chamber, and both of an elevation angle and adepression angle of a ejected flame are adjusted to 45 degrees.
 9. Anair bag apparatus comprising a gas generator, an impact sensor detectingan impact to activate the gas generator, an air bag introducing a gasgenerated in the gas generator to inflate, and a module caseaccommodating the gas generator, wherein the gas generator for an airbag is a gas generator according to claim
 1. 10. A gas generator for anair bag comprising: a housing having a gas discharging port; asubstantially cylindrical inner cylindrical member disposed in thehousing; an ignition means accommodating chamber for accommodating aignition means defined inside the inner cylindrical member; a combustionchamber for accommodating gas generating agent defined outside the innercylindrical member; and plural communicating portions circumferentiallyformed on the circumferential surface of the inner cylindrical member tocommunicate the ignition means accommodating chamber with the combustionchamber, wherein the central angle formed by the adjacent communicatingportions is not less than 60 degrees, the communicating portioncomprises at least one flame-transferring hole radially penetrating theinner cylindrical member, and the flame-transferring hole is formed tohave the inner diameter of 1 to 4mm.
 11. The gas generator for an airbag according to claim 10, wherein the communicating portion comprisesat least two flame-transferring holes radially penetrating in the innercylindrical member.
 12. A gas generator for an air bag comprising; ahousing having a gas discharging port; a substantially cylindrical innercylindrical member disposed in the housing; an ignition meansaccommodating chamber for accommodating an ignition means defined insidethe inner cylindrical member; a combustion chamber for accommodating agas generating agent defined outside the inner cylindrical member, andplural flame-transferring holes for ejecting a flame generated byactivation of the ignition means into the combustion chamber, whereinthe plural flame-transferring holes are formed on the circumferentialsurface of the inner cylindrical member, and the flame-transferringholes eject a flame, generated by activation of the ignition means intothe combustion chamber, at 45 degree of elevation angle and depressionangle, the flame-transferring hole is formed to have the inner diameterof 1 to 4mm, and the flame-transferring holes are radially formed on thecircumferential surface of the inner cylindrical member, and the centralangle formed by the adjacent communicating portions being not less than60 degrees.
 13. A gas generator for an air bag comprising: a housinghaving a gas discharging port; a substantially cylindrical innercylindrical member disposed in the housing; an ignition meansaccommodating chamber for accommodating an ignition means defined insidethe inner cylindrical member; a combustion chamber for accommodating agas generating agent defined outside the inner cylindrical member; andplural flame-transferring holes for ejecting a flame generated byactivation of the ignition means into a first combustion chamber,wherein the plural flame-transferring holes are formed on thecircumferential surface of the inner cylindrical member, and theflame-transferring holes are formed at a distance of 30% to 70% of theaxial length of the inner cylindrical member, from an end of the innercylindrical member, the flame-transferring holes being formed on thecircumferential surface of the inner cylindrical member, and the centralangle formed by the adjacent flame-transferring holes being not lessthan 60 degrees.
 14. The gas generator for an air bag according to claim13, wherein the plural flame-transferring holes are formed at a distanceof 40% to 60% of the axial length of the inner cylindrical member, froman end of the inner cylindrical member.
 15. The gas generator for an airbag according to claim 13 or 14, wherein an igniter which is activatedwhen an ignition electric current for activation is applied in one axialend side of the inner cylindrical member, and the pluralflame-transferring holes are formed in the end being opposite, dividedwith respect to the axial center of the inner cylindrical member. 16.The gas generator for an air bag according to claim 13, wherein theignition means accommodating chamber accommodates an ignition meansincluding an igniter which is activated when an ignition electriccurrent is applied, the plural flame-transferring holes ejecting a flamegenerated by activation of the ignition means into the combustionchamber are circumferentially formed on the circumferential surface ofthe inner cylindrical member, and the horizontal angle of an ejectingflame from the flame-transferring holes is adjusted to not less than 60degrees having, as the center, the axis perpendicular to the center ofthe flame-transferring holes.
 17. The gas generator for an air bagaccording to claim 13, wherein the ignition means accommodating chamberaccommodates an ignition means including an igniter which is activatedwhen an ignition electric current is applied, the combustion chamberaccommodates a gas generating agent ignited and burnt by activation ofthe ignition means to generate a combustion gas, and the pressure insidethe housing reaches its maximum at 5 to 20 milliseconds after theignition electric current is applied.
 18. A gas generator for an air bagcomprising; a housing having a gas discharging port; a substantiallycylindrical inner cylindrical member disposed in the housing; anignition means accommodating chamber for accommodating an ignition meansdefined inside the inner cylindrical member; and a combustion chamberfor accommodating a gas generating agent defined outside the innercylindrical member, and plural communicating portions circumferentiallyformed on the circumferential surface of the inner cylindrical member tocommunicate the ignition means accommodating chamber with the combustionchamber, wherein the central angle formed by the adjacent communicatingportions is not more than 60 degrees.
 19. The gas generator for an airbag according to claim 18, wherein the communicating portion comprisesone or at least two flame-transferring holes radially penetrating in theinner cylindrical member.
 20. The gas generator for an air bag accordingto claim 19, wherein the communicating portion comprises oneflame-transferring hole radially penetrating in the inner cylindricalmember, and the flame-transferring hole is formed to have the innerdiameter of 1 to 4mm.
 21. The gas generator for an air bag according toany one of claim 1, 10, 12, 13 and 18, wherein, the central angle formedby the adjacent communicating portions or flame-transferring holes is 90degrees or higher.
 22. The gas generator for an air bag according to anyone of claim 1, 10, 12, 13 and 18, further comprising a deflectingmember which has a cylindrical portion and which is disposedcircumferentially between said combustion chamber and said dischargeport.
 23. A method for obtaining an S-shaped tank curve from a gasgenerator during a tank combustion test, comprising: providing the gasgenerator of any one of claims 1, 10, 12 and 18; activating the ignitionmeans by applying an ignition electric current; and setting parametersof the gas generator such that the tank pressure the tank pressuremeasured at 0.25×T (milliseconds) is not more than 0.25×P(kPa) and thetank pressure measured at 0.80×T (milliseconds) is not less than0.70×P(kPa), wherein P represents the maximum tank pressure (kPa), and Trepresents a period of time from the start of rising of the tankpressure to the time when the maximum tank pressure P(kPa) has beenreached (milliseconds) in tank combustion test.
 24. A method forobtaining an S-shaped tank curve meeting parameters that the tankpressure the tank pressure measured at 0.25×T (milliseconds) is not morethan 0.25×P(kPa) and the tank pressure measured at 0.80×T (milliseconds)is not less than 0.70×P(kPa) during a tank combustion test from a gasgenerator, comprising: providing the gas generator of any one of claims1, 10, 12, 13 and 18; and activating the ignition means by applying anignition electric current.
 25. A method to inflate an air bag,comprising: providing the gas generator of any one of claims 1, 10, 12and 18; activating the ignition means by applying an ignition electriccurrent; and setting parameters of the gas generator such that the tankpressure the tank pressure measured at 0.25×T (milliseconds) is not morethan 0.25×P(kPa) and the tank pressure measured at 0.80×T (milliseconds)is not less than 0.70×P(kPa), wherein P represents the maximum tankpressure (kPa), and T represents a period of time from the start ofrising of the tank pressure to the time when the maximum tank pressureP(kPa) has been reached (milliseconds) in tank combustion test.